1. Field
Various embodiments of the present invention relate generally to a circuit for generating a periodic signal and a memory device including the same.
2. Description of the Related Art
A memory cell of a memory device may include a transistor serving as a switch and a capacitor for storing a charge (data). Depending on whether a charge may be stored in the capacitor of the memory cell, for example, depending on whether a terminal voltage of the capacitor is high or low, it is determined whether the logic level of the stored data is high (logic 1) or low (logic 2).
Since data is stored in the form of accumulated charges in the capacitor of a memory cell, theoretically there is no power consumption for maintaining stored data. However, an initial charge stored in the capacitor may diminish due to a leakage current and as a result data may be lost. For preventing such data loss, data stored in the memory cells of a memory device are typically read periodically before the data are lost and the capacitors of the memory cells are recharged according to the read data. This operation is commonly known as a refresh operation.
Typically, a refresh operation is a self-refresh operation performed independently from other operations in a memory device. The period of the self-refresh operation is optimized for the memory device depending upon the retention time of the memory cell. For example, when the memory device has a long retention time the refresh operation period is lengthened to reduce current consumption, whereas when the memory device has a short retention time, the refresh operation period is shortened to minimize data loss. The retention time of a memory device is generally affected by the temperature in which the memory device operates.
Hence, it would be advantageous to employ an oscillator for generating a periodic signal having a period which varies depending on the temperature for adjusting the refresh operation period of a self-refresh operation of a memory device. However, heretofore, such technology is not sufficiently precise.
Hence further improvements for reducing or preventing data loss due to current leakage and also for reducing the overall power consumption of a memory device are needed. Also, an improved technology for precisely adjusting the period of a periodic signal as a function of temperature, is required.